The present invention relates to winglets, and, more particularly, to a wing of a ground effect vehicle having a winglet with negative dihedral angle and variable sweep.
Ground effect vehicles have been developed in both fields of aeronautics and marine craft. Ground effect vehicles are those vehicles which receive reduced drag due to the reduction of wing-tip vortices while traveling at low altitudes near ground, and more typically, near water. The closer the wing tip is to the ground or water, the lower the drag.
Ground effect vehicles generally comprise marine craft and aircraft. The two are typically distinguished by those that can sustain extended flight without the aid of ground effect (aircraft) and those that cannot (marine craft). The International Civil Aviation Organization (ICAO) and International Maritime Organization (IMO), both organizations of the United Nations, jointly exercise jurisdiction over these vehicles. The ICAO and IMO have also united to develop uniform navigation and safety rules for these types of vehicles, expected to be published by the year 2004.
The marine engineering arts have developed ground effect craft that either induce ground effect, such as hovercraft, or utilize some benefits of ground effect in combination with hydrodynamic hull and fin arrangements, such as catamarans and hydrofoils. Other maritime ground effect aircraft are being developed, and typically include ground effect wings to provide greater stability and lift. They cannot, however, sustain flight without maintaining close distance to the ground.
The aeronautical engineering arts have also advanced ground effect vehicles beginning with the Russian Ekranoplan KM, also known as the Caspian Sea Monster, which was developed in the 1960s for cargo transport and missile delivery applications. The KM uses extended wings with negative dihedral winglets on each end in order to promote the ground effect. The negative dihedral winglets are generally allowed to touch water if the KM is unintentionally flown too low. However, allowing the winglets to touch the water substantially increases drag, and may damage the wing or winglets. As such, the structural weight of the wing must be increased to account for water loads. If too much of the winglets contact water, the airplane may also experience stability problems.
It is typical for ground effect vehicles to travel within a few feet of the sea. In general, drag is reduced when the distance between the wingtip and the ground or water is reduced. in high wave conditions, altitude must be increased to avoid a collision between the wings or winglets and the water. Positive dihedral winglets on ground effect vehicles are effective in reducing drag, but not as effective as winglets that allow for decreased height between the lowest point on the wingtip to the water or ground. Additionally, ground effect vehicles with negative dihedral winglets may face the problem of winglet contact with the ground or water during landing and takeoff. As such, there exists a need in the art for ground effect vehicles with negative dihedral angles that can temporarily increase ground clearance or water clearance on the winglets, thus avoiding impact with the ground or water.
To meet these and other needs, a ground effect vehicle and ground effect wing with a negative dihedral winglet are therefore provided. The ground effect wing includes a fixed wing capable of being attached to a ground effect vehicle fuselage. At the outward extension of the wing, a winglet is attached with a negative dihedral angle. The winglet is attached about a hinge or other mechanism so that it may rotate about a pivot axis. The pivot axis is generally defined at an angle that is roughly perpendicular to the direction of flight. This angle is also roughly normal to the plane of the winglet. The plane of the winglet is here defined by a flat surface between the leading and trailing edge of the winglet. In one such embodiment, the pivot axis is substantially perpendicular to the chord of the fixed wing. As such, the rotation of the winglet about the pivot axis results in variation of the winglet ground clearance through a range of sweep angles.
In several advantageous embodiments, an actuator is connected to the winglet in order to position the winglet through the range of sweep angles. Such actuators may include hydraulic actuators, springed actuators, rotating ballscrew actuators or other such actuators known to those skilled in the art. One advantageous embodiment includes an actuator with stored energy that may be activated in order to actuate the winglet through rotation about the pivot axis toward an aft sweep angle. A locking mechanism is included to lock the winglet in place against the stored energy actuator such that as the locking mechanism is unlocked the stored energy actuator automatically actuates the winglet through aft rotation. One embodiment of the locking mechanism includes a ratcheting mechanism. The ratcheting mechanism also permits rotation of the winglet about the pivot axis in order to change the sweep angle to avoid impact with an object such as the ground or water. Other embodiments for actuating the winglet through aft rotation include an aerodynamic device, such as a control surface or movable flap. The aerodynamic device is controlled to increase drag on the winglet such that the drag translates to rotational force about the pivot axis. Thus, the rotational force induces the winglet to position an aft sweep angle. In one embodiment, the rotational force caused by the drag is controlled by a locking mechanism. Thus, the winglet will increase sweep aft, thereby increasing clearance between the ground or water. As such, the winglet avoids contact with ground or water, consequently avoiding the stability problems or structural problems that would otherwise be caused from the impact.
Another advantageous embodiment of the present invention includes a ground effect vehicle comprising a fuselage and at least one ground effect wing. The ground effect wing is typically a wing with one end attached to the fuselage between the forward and aft portions of the fuselage and a winglet attached to the outer periphery of the second end of the fixed wing. The winglet is attached so as to form a negative dihedral angle and to be positionable through a range of sweep angles about a pivot axis, the pivot axis being defined at an angle with respect to the plane of the winglet. According to one embodiment, the pivot axis will be substantially perpendicular to the plane of the winglet. One embodiment of the ground effect vehicle includes actuators for actuating the winglet through the range of aft sweep angles. Such actuators may include hydraulic assisted actuators, spring assisted actuators or other actuating mechanisms known to those skilled in the art. Such actuators are generally controlled by flight control systems adapted to control the actuator and vary the sweep of the winglet to a desired position.
Several embodiments of the ground effect vehicle include sensors to determine whether an object lies in the path of the winglet. As such, the sensors are in communication with the flight control system to provide advance warning to the flight control system of an impending impact. Accordingly, the flight control system is adapted to vary the sweep of the winglet in order to increase the clearance from the ground or water to avoid impact. In certain embodiments, these sensors include forward looking sensors such as radar, laser, infrared, acoustic and imaging sensors. Another embodiment of the ground effect vehicle comprises physical sensors including an elongate member with a first end attached to the ground effect wing and second end extending downwardly therefrom. Such physical sensors are commonly known to those skilled in the art and referred to as xe2x80x9cfeelers.xe2x80x9d In either embodiment, a physical sensor or an electromagnetic sensor provides signals either to the flight control system or directly to the actuators on the winglet in order to immediately vary the sweep of the winglet in order to avoid impact with the sensed object.
Therefore, a ground effect vehicle with a ground effect wing having a variable sweep winglet advantageously permits increasing clearance of the winglet tip from ground or water by actuating the winglet to a further aft sweep. As such, control of the winglet can be maintained in order to avoid contact of the winglet with ground or water, thereby avoiding structural or stability problems. Consequently, the ground effect vehicle may advantageously maintain flight altitude for most efficient travel in ground effect.